function Base64() {
    
       // private property
       _keyStr = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/=";
    
       // public method for encoding
       this.encode = function (input) {
           var output = "";
           var chr1, chr2, chr3, enc1, enc2, enc3, enc4;
           var i = 0;
           input = _utf8_encode(input);
           while (i < input.length) {
               chr1 = input.charCodeAt(i++);
               chr2 = input.charCodeAt(i++);
               chr3 = input.charCodeAt(i++);
               enc1 = chr1 >> 2;
               enc2 = ((chr1 & 3) << 4) | (chr2 >> 4);
               enc3 = ((chr2 & 15) << 2) | (chr3 >> 6);
               enc4 = chr3 & 63;
               if (isNaN(chr2)) {
                   enc3 = enc4 = 64;
               } else if (isNaN(chr3)) {
                   enc4 = 64;
               }
               output = output +
               _keyStr.charAt(enc1) + _keyStr.charAt(enc2) +
               _keyStr.charAt(enc3) + _keyStr.charAt(enc4);
           }
           return output;
       }
    
       // public method for decoding
       this.decode = function (input) {
           var output = "";
           var chr1, chr2, chr3;
           var enc1, enc2, enc3, enc4;
           var i = 0;
           input = input.replace(/[^A-Za-z0-9\+\/\=]/g, "");
           while (i < input.length) {
               enc1 = _keyStr.indexOf(input.charAt(i++));
               enc2 = _keyStr.indexOf(input.charAt(i++));
               enc3 = _keyStr.indexOf(input.charAt(i++));
               enc4 = _keyStr.indexOf(input.charAt(i++));
               chr1 = (enc1 << 2) | (enc2 >> 4);
               chr2 = ((enc2 & 15) << 4) | (enc3 >> 2);
               chr3 = ((enc3 & 3) << 6) | enc4;
               output = output + String.fromCharCode(chr1);
               if (enc3 != 64) {
                   output = output + String.fromCharCode(chr2);
               }
               if (enc4 != 64) {
                   output = output + String.fromCharCode(chr3);
               }
           }
           output = _utf8_decode(output);
           return output;
       }
    
       // private method for UTF-8 encoding
       _utf8_encode = function (string) {
           string = string.replace(/\r\n/g,"\n");
           var utftext = "";
           for (var n = 0; n < string.length; n++) {
               var c = string.charCodeAt(n);
               if (c < 128) {
                   utftext += String.fromCharCode(c);
               } else if((c > 127) && (c < 2048)) {
                   utftext += String.fromCharCode((c >> 6) | 192);
                   utftext += String.fromCharCode((c & 63) | 128);
               } else {
                   utftext += String.fromCharCode((c >> 12) | 224);
                   utftext += String.fromCharCode(((c >> 6) & 63) | 128);
                   utftext += String.fromCharCode((c & 63) | 128);
               }
    
           }
           return utftext;
       }
    
       // private method for UTF-8 decoding
       _utf8_decode = function (utftext) {
           var string = "";
           var i = 0;
           var c = c1 = c2 = 0;
           while ( i < utftext.length ) {
               c = utftext.charCodeAt(i);
               if (c < 128) {
                   string += String.fromCharCode(c);
                   i++;
               } else if((c > 191) && (c < 224)) {
                   c2 = utftext.charCodeAt(i+1);
                   string += String.fromCharCode(((c & 31) << 6) | (c2 & 63));
                   i += 2;
               } else {
                   c2 = utftext.charCodeAt(i+1);
                   c3 = utftext.charCodeAt(i+2);
                   string += String.fromCharCode(((c & 15) << 12) | ((c2 & 63) << 6) | (c3 & 63));
                   i += 3;
               }
           }
           return string;
       }
   }